Non-circular high q coils

ABSTRACT

A low cost, high Q mounted coil consisting of a non-circular, close wound coil having a turn length substantially longer than the circumference of the inscribed cylinder thereof mounted on a cylindrical coil form.

United States Patent Renskers [4 1 July 1 1, 1972 s41 NON-CIRCULAR HIGH Q COILS 1,604,478 10/1926 Orton ..336/225 x 1,615,755 l/1927 Grave ..336/l89 X [721 kenske's' Crystal Lake 1,679,471 8/1928 Hill ..336/191 x [73] Assignee: Collcraft, Inc., Cary, 111. 1,680,415 8/1928 l-lengstenberg. .....336/ 191 X 1,906,812 5/ 1933 Rowell ..336/225 X 1 1 Flledi May 12, 1971 1,984,433 12/1934 Runge ..336/l89 [211 App]. No: 142,723 3,169,234 2/1965 Remskers ..336/192 Related US Application Data FOREIGN PATENTS OR APPLICATIONS 566,894 11/1923 France ..336/189 [63] gg xggz g zg 938,079 3/1948 France ..336/l89 234,635 1925 Great Britain ..336/ l 90 52 U.S. c1 ..336/189, 336/136, 336/191, 256'028 Great "336/ 190 336/225 Prima l ry Examiner-Thomas J. Kozma [51 Int. Cl. y e lp & Rogers [58] Field of Search 336/189, 190, 191, 225, 226,

336/227, 228, 136, 192 57 ABSTRACT 56] References Cited A low cost, high Q mounted coil consisting of a non-circular, close wound coil having a turn length substantially longer than UNITED STATES PATENTS the circumference of the inscribed cylinder thereof mounted on a cylindrical coil form. 1,409,352 3/1922 Adair ..336/191 1,585,389 5/1926 Judd et al. ..336/l90 7 Claims, 14 Drawing Figures Patented July 11, 1972 I 3,676,813

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 812,836 of John O. Renskers titled NON-CIRCULAR HIGH Q COILS filed Apr. 2, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to single layer, close wound, non-circular, high Q solenoid type windings.

2. Description of the Prior Art In such coils as those employed in absorption traps at 41.25 and 47.25 MHz in television I.F. amplifiers, it is, of course, essential that the coil of the trap circuit has a certain minimum Q for sharpness of tuning and a sufficiency of absorption. The conventional arrangement heretofore has been to mount an IF circuit coil adjacent to the flange of a conventional flanged quarter-inch coil form (actually 0.287 inches CD.) of extended length and to mount the trap coil and its resonating capacitor on the extended part of the form optimally spaced from the circuit coil for energy absorption at the desired coupling level. Each of these coils will have its individual, individually adjustable tuning slug contained within the form.

Coils of acceptably high Q have been made by space-winding wire, for instance, of gauge to fit closely and desirably frictionally the exterior of a quarter-inch form. As a practical matter, however, such coils must be wound on a mandrel, removed therefrom, and mounted on the form. In the course of the removal and the mounting, the coils are apt to become compressed or stretched, and it is exceedingly difficult to hold such coils to any desired effective length and thus to predictable values. If the coils could be wound with turns contiguous, this problem could be effectively eliminated.

To obtain the desired Q in a close wound coil the practice has been to employ coils about 0.40 to 0.60 inches in diameter. The Q improvement results both from the larger diameter and from the greater spacing of the coil from the tuning slug which at television I.F. frequencies is usually a lossy device. The Q of such a coil (or trap circuit) is on the order of 175 to 200 as opposed to a close wound coil proportioned to this coil form diameter which would have a Q of 90 to 120. This latter span of figures is inadequate to absorb efficiently the adjacent channel sound frequencies.

In order to mount the larger diameter coil to the quarterinch form, a sleeve of a size to engage the inside of the trap coil must be cemented to the periphery of the form in the vicinity of optimum trap coil coupling. This involves an additional component of the assembly and an additional manufacturing step, both of which add substantially to the cost of such circuitry.

Cost savings are the very essence of those businesses supplying the radio and television industries. By the elimination of the sleeve and the additional operation involved mounting it to the form, a cost saving of a minimum of 10 percent could be achieved, and it could run as high as 50 percent or more in lower volume applications where molded sleeves are unfeasible or in applications where particularly precise and stable dialectric values are important.

SUMMARY OF THE INVENTION This invention contemplates close winding coils of the character described on non-circular mandrels such as triangular, rhomboidal, elliptical, etc., such that a turn of the coil wound thereon has an inscribed circle adapted to embrace closely the exterior of a quarter inch or other standard coil form but has a circumscribed circle substantially larger. It has been found that a coil so wound has a Q only slightly less than a circular coil having equal turn length; sufficiently close such that it may be practicably substituted for the circular coil without, however, the interpositioning of a sleeve on the form.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an input I.F. coil with trap, embodying the invention;

FIG. 2 is a top plan view of the trap coil of FIG. 1;

FIG. 3 is a side elevation of a similar coil adapted differently for circuit connection;

FIG. 4 is a perspective view of a mandrel of a winding machine illustrating the method of making the coil of FIGS. 1 through 3;

FIG. 5 is a side elevation of a mounted inductor coil having a slightly different configuration from the trap coil of FIG. 1;

FIG. 6 is a top plan view of the coil of FIG. 5; FIG. 7 illustrates a method of making the coil of FIGS. 5 and FIG. 8 is a somewhat diagrammatic top plan view analogous to FIG. illustrating an optional form of coil enjoying the same advantages as the coil of FIG. 1;

FIG. 9 is a top plan view similar to FIG. 8 illustrating another optional form of coil;

FIG. 10 is a diagrammatic end elevation of a mandrel similar to that illustrated in FIG. 4 with associated tooling for forming the coil of FIG. 9;

FIG. 11 is a top plan view similar to FIG. 8 illustrating yet another form of coil;

FIG. 12 is a diagrammatic end elevation of apparatus for making the coil of FIG. 1 1, shown open;

FIG. 13 is a view similar to FIG. 12 showing the apparatus in the formed coil configuration; and

FIG. 14 is an end elevation of a coil winding mandrel for making the coil configuration of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A representative, quarter inch coil form 10 is illustrated in FIG. 1. It consists of a tube 12 having an outside diameter of 0.287 inch and an integral skirt 14 at the lower end thereof which serves to anchor coil leads and terminal connections in a fashion such that the terminal connections or coil leads extend below the skirt. The tube 12 is thin walled and commonly has longitudinal ribs on the inside surface thereof to contain adjustably a pair of quarter-inch threaded, individually adjustable, tuning slugs l5 and 16. A form of this character is illustrated in US. Pat. No. 3,169,234 issued Feb. 9, 1965, to John O. Renskers.

This coil form is one of a few which has been accepted as an industry standard. Dies are plentiful and generally have long since been amortized. Thus, the forms are widely and cheaply available and their use is indicated wherever possible.

An I.F. circuit coil 11 wound to fit the form tube 12 snugly is mounted on the tube adjacent the flange or skirt 14 with the integral leads 13 thereof extending through the skirt 14 for cir cuit connection. Slug 15 is associated with coil 11 for tuning. Coil 11 in association with slug 15 is relatively low Q for broadness of tuning.

The trap coil 18 is mounted to the form upwardly of the coil 11 and consists of a series of approximately triangular turns 20. The turns are defined as only approximately triangular in that the sum of the angles of each of the turns is slightly greater than 180 and thus the apices 22 of the consecutive turns define spiral lines about the axis of the form 10. The triangular turns are proportioned to embrace closely and engage frictionally the exterior of the tube 12. It will thus be appreciated that the inscribed circle of each coil turn or the inscribed cylinder of the collective turns will be equal to the exterior cylinder of the tube. In practice, the coil may be wound slightly undersized with respect to the tube to insure a frictional bearing of the coil on the tube. Such undersize may also cause an unwinding of the coil so as to obtain the consecutive angular displacement of the turns of the coil from each other.

Since adjacent turns of the coil are not aligned, distributed sewhere are spaced variably up to a substantial separation. A capacitor 21 is connected across the leads 23 of the trap coil to complete the resonant trap circuit. The slug 16 serves to tune the trap circuit to the precise frequency to be absorbed. In other words, by virtue of the non-circularity of the coil there is provided a close-wound coil with its attendant manipulative and manufacturing advantage mountable on a small coil form and having a Q the close equivalent of a sleeve mounted large diameter close-wound coil or of a form-fitting, space-wound coil.

FIG. 4 is illustrative of a method of producing the coil shown in FIGS. 1 and 2. In that figure, a three-lobed mandrel 34 is substituted for the ordinary cylindrical mandrel of the conventional winding machine. The lobes 36 are desirably smooth and round edged so that the wound coil may be easily removed from the mandrel. The winding will, of course, be conducted under substantial tension as is the general practice in coil winding. The wire will be fed to the mandrel from an appropriate source of supply 38 over appropriate guides 40. When the desired number of turns have been laid down on the mandrel, the wire will be cut to provide the necessary finished lead length and the coil withdrawn from the mandrel, at which time it will spring back to its spirally oriented sequence of triangular turns.

The degree of spring back will depend generally on the hardness of the wire. For instance, with soft wire there may be very little spring back, whereas with seven turns of a hard wire, the sequential spring back may amount to as much as 120 as between the uppermost and the lowermost turn. As pointed out above, however, the fit between the coil and the form can impose a greater angular displacement on a coil, regardless of hardness.

It is desirable that the assembly of the coil to the form not rest purely on the basis of a frictional engagement. Ac-

cordingly, the coil will preferably be cemented to the tube 12 of the form. v

The coil proper illustrated in FIG. 1 and manufactured according to the method of FIG. 4 may be otherwise employed as shown in FIG. 3. Here the coil leads 42 and 44 are simply unbent end extensions of the first and the last turns of the coil proper 46, and the leads themselves are directly adapted for insertion into a printed circuit or other circuit connection. As illustrated, a simple tubular coil form 48 is contained within the central aperture or inscribed cylinder of the coil in the same fashion as the tube 12 of coil form of FIG. 1, to support a tuning slug 50. In this configuration, the use of the coil as an air core coil in such function as a loading coil, for instance, will be appreciated, and the form 48 may be wholly omitted. It is likewise conceivable that the form 48 may be omitted and the tuning slug 50 be engaged directly by the turns of the wire. Such usage would require an abrasion-proof insulation between the wire and the tuning slug or a utilization demanding a minimum of tuning adjustment, but such capability is distinctly within the purview of this invention.

FIGS. 5, 6 and 7 illustrate a coil very similar to that shown in FIG. 1 without, however, the angular offset between adjacent turns. A coil of this character may be formed, for instance, by winding a conventional circular coil 52 (FIG. 7) of the character shown in U.S. Pat. No. 3,l69,234 and then flattening the sides by the simultaneous advance of fiat-faced movable dies 54 spaced 120 from each other against the periphery of the coil supported by a triangular anvil 56. A coil so formed will evidently have no tendency to unwind as in the case of the first described coil.

Of course, should this manufacturing procedure be preferred for any reason and it still be desired that the coil unwind, the inscribed circle of the coil may, again, be made undersized with respect to the form, so forcing the unwinding. In either case, the coil will be mounted to a form 58 and the leads 60 thereof be extended through the skirt 62 of the form.

Coils of this character or of the trap of FIG. 1 are generally pointed to usage within the to 200 MHz range. As such, wire on the order of 20 gauge, for instance, is an appropriate size. Such wire, wound, is shape-retaining and capable of providing its own terminal connections. Thus the leads depart from the coil parallel to the axis of the coil, and extend down to and through the skirt 14 to constitute the terminal connections 60 in the fashion taught, for instance, in the aforesaid U.S. Pat. No. 3,169,234.

The mounted coil 65 shown in FIG. 8 is substantially the same as the trap coil shown in FIG. 1 except that this coil is wound on a rhomboidal mandrel rather than a triangular one. By such formation, the linear length of each coil turn can be considerably extended over that of the triangular structure and at the same time a precisely defined inscribed cylinder will be created for accurate location of the coil on the form 66. Analogous coils could be formed by winding on elliptical or lenticular mandrels.

A coil configuration which provides for a still greater extension of linear turn length without going to an excessively great circumscribed circle is the modification illustrated in FIGS. 9 and 10. Here the coil 68 is star-shaped or stellate with a re-entrant angle or concavity 70 between each of the apices 72 of the coil turn. The inscribed circle of such a figure, of course, will be one tangent to the re-entrant angles. A coil of this configuration may illustratively be formed by winding a conventional single layer close wound coil, and then, as illustrated in FIG. 10, mounting the coil 68 on a three-lobed anvil 74, similar in end elevation to the mandrel 34 of FIG. 4, and deforming the coil turns inwardly between the lobes 76 by the simultaneous inward advance of arcuate dies 78. Although such formation will not inherently give an angular offset of the consecutive turns, this effect can be obtained if desired by, again, making the inscribed circle slightly undersized with respect to the form 80 on which the coil is mounted. The mounting again may be the same in all respects as illustrated in FIGS. 1 or 5.

FIGS. 11, I2, 13, and 14 illustrate still another modification. Here the coil 82 is keyhole shaped, each coil turn consisting of a partial circle 84, greater however than 180, and a lobe 86 extending outward therefrom. A coil of this character may be formed by winding an ovate coil 88 on a cylindrical mandrel 89 having a lateral extension 91 thereon. That coil is placed over a post of the size of the coil form, and a pair of dies 92 which together define the desired arc length of the inscribed circle on the coil are advanced against the post 90 and to permit the excess of coil length to obtrude from the gap between them to form the lobes 86. Other nonsymmetrical forms of coil lend themselves to the same treatment. The ovate coil 88 of FIG. 14 could be used without modification. It will be appreciated that each turn of the coil 88 wound thereon will have more than a 180 engagement on a coil form.

From the foregoing description it will be appreciated that a category of coil has been described here with the advantage of a large effective diameter, which nevertheless is capable of being mounted on and carried by a standard coil form of substantially less diameter simply and inexpensively. An oversized circular coil could be mounted on a form by the use of an interposed sleeve, but such an expedient would be considerably more expensive than the direct mounting described here. Furthermore, there is the capability of close winding the coil with all its attendant advantages. The angular displacement of the turns incident to the unwinding thereof, normal or forced as discussed above will also give some of the advantages of a space wound coil. This is an inherent characteristic of a non circular coil, and the natural unwinding is an inherent consequence of making the coil by winding it on a noncircular mandrel.

From the foregoing, it will be appreciated that, by the use of noncircularity, a high Q coil may be mounted for circuit inclusion in exceedingly inexpensive fashion. The Q of the trap circuit illustrated in FIG. 1 will not be quite the equal of a circuit incorporating a'circular coil of equal outside diameter, to 185 as compared to to 200, but in the context of this trap circuit the Q is sufficient. It is notably superior to that of a close wound circular coil fitted to the form. The turn length of the shortest described form or the form most limited as to length, the equilateral triangular form, is theoretically 65 percent greater than that of a fitted circular coil. In practice, the ratio will be slightly less, about 60 percent, by virtue of the rounding of the corners and the opening up of the coil might further reduce the ratio to 50 percent. This least ratio, however, is still superior to the 0.40 inch diameter circular coil mentioned above as presently employed in absorption sound traps.

Likewise, the noncircular coil minimizes the reduction of Q attributable to the adjacency to the tuning slug. Three small elements of the developed triangular coil and their associated lines of force are tangent to the form and thus as near the core as a fitting coil would be. Substantially, the greater proportion is more remote and less closely coupled to the slug. Hence fewer flux lines of the coil are affected by the hysteresis losses of the tuning slug.

The above remarks are directed to the simplest, but least advantageous of the illustrated configurations. The other configurations provide scope for a considerably greater ratio between turn length and inscribed diameter.

As stated above, the intent of the invention is largely economic; to mount a high Q coil inexpensively. Accordingly, the invention is directed to coils having a comparable low cost of manufacture. Mandrel winding or winding performed by drawing from a source of wire supply onto and by a rotating mandrel is by all odds the least expensive method of coilwinding, and the term solenoid winding in the claims here is intended to limit this invention to coils having a configuration characteristic of such formation; a simple helix with identical aligned turns in the winding thereof, each turn constituting a single, simple, closed geometrical figure.

Also, this invention is sensible primarily in the context of a standard coil form. By trade usage, a few stock sizes of coil form have been adopted, available from many molders or suppliers from inventory. The quarter inch form has been described. Others are a No. form to accommodate a No. 10

screw gauge tuning slug; similarly, a No. 8 and a No. 6 form.

All of these forms have exterior diameters to provide a wall about 0.015 inch thick. This invention is applicable to any of these, of course. The significant factor is that the form be a standard or stock form.

The invention has utility in conjunction with non-standard forms in such instances as the input l.F. coil with trap, illustrated, where a close fitting coil must be placed on the form first, and a second large turn length coil placed on the form in coupled relationship with the first coil. Obviously, the close fitting coil could not be applied over a support for the larger coil.

Finally, although the invention has been described particularly in the specific context of an adjacent channel sound trap, it will be understood that it is applicable wherever a low cost high Q coil is desired, as illustrated, for instance, in FIGS. 3 and 5 in such utilization as loading coils, oscillators, choke coils, etc.

I claim:

1. A mounted high Q coil comprising a single layer, closewound, noncircular solenoid winding and a cylindrical-surfaced coil form fitted within the inscribed cylinder of said winding, said inscribed cylinder being proportioned so that said winding engages said surface frictionally, the inscribed circle of each turn thereof being an element of the surface of said inscribed cylinder, said winding having a turn length at least half again greater than that of a cylindrical coil fitted to said form.

2. The combination as set forth in claims 1 wherein the turns of said coil have a triangular configuration.

3. The combination as set forth in claims 1 wherein the turns of said coil have a configuration having substantially different major and minor axes.

4. The combination as set forth in claims 1 wherein the turns of said coil have a stellate configuration with reentrant angles between the apices thereof, said reentrant angles collectively defining said inscribed cylinder.

5. The combination as set forth in claim 1 wherein the inscribed circle of any of said turns is tangent to said turn at a point on said turn transverse across the coil wire to a point where the circumscribed circle is tangent.

6. An absorption trap assembly comprising a coil form having a cylindrical surface of uniform diameter, a relatively low Q, circular, close-wound coil fitted on said surface, and a high Q coil comprising a single layer, close-wound, non-circular winding having an inscribed cylinder equal to that of said low Q coil and a turn length substantially greater than that of said low Q coil fitted on said surface in coupled, energy absorbing relation with said low Q coil.

7. The combination of claim 1 wherein the turns of said coil are unsupported other than at the points of engagement on said form except for such support as said turns may derive from adjacent turns. 

1. A mounted high Q coil comprising a single layer, close-wound, noncircular solenoid winding and a cylindrical-surfaced coil form fitted within the inscribed cylinder of said winding, said inscribed cylinder being proportioned so that said winding engages said surface frictionally, the inscribed circle of each turn thereof being an element of the surface of said inscribed cylinder, said winding having a turn length at least half again greater than that of a cylindrical coil fitted to said form.
 2. The combination as set forth in claims 1 wherein the turns of said coil have a triangular configuration.
 3. The combination as set forth in claims 1 wherein the turns of said coil have a configuration having substantially different major and minor axes.
 4. The combination as set forth in claims 1 wherein the turns of said coil have a stellate configuration with reentrant angles between the apices thereof, said reentrant angles collectively defining said inscribed cylinder.
 5. The combination as set forth in claim 1 wherein the inscribed circle of any of said turns is tangent to said turn at a point on said turn transverse across the coil wire to a point where the circumscribed circle is tangent.
 6. An absorption trap assembly comprising a coil form having a cylindrical surface of uniform diameter, a relatively low Q, circular, close-wound coil fitted on said surface, and a high Q coil comprising a single layer, close-wound, non-circular winding having an inscribed cylinder equal to that of said low Q coil and a turn length substantially greater than that of said low Q coil fitted on said surface in coupled, energy absorbing relation with said low Q coil.
 7. The combination of claim 1 wherein the turns of said coil are unsupported other than at the points of engagement on said form except for such support as said turns may derive from adjacent turns. 